1. Field of the Invention
The present invention relates to microwave transceivers, and more particularly to microwave radar sensors, such as rangefinders and motion detectors.
2. Description of Related Art
Radio and radar transceivers operate at radio frequency (RF) wavelengths that are larger than the active devices used to generate the RF. Active devices, such as vacuum tubes and transistors, are considered to be “beyond cutoff” when subjected to frequencies having a wavelength approaching their physical dimensions or the dimensions of their connection leads. Operation at such short wavelengths is nearly impossible since a quarter-wavelength lead forms a transformer that inverts the impedance from low to high or vice-versa. In contrast, antennas need to be a significant fraction of a wavelength, such as a quarter-wavelength, for efficient radiation into free space.
Small inductors can radiate with limited effectiveness for applications such as automotive remote door-lock transmitters. For example, U.S. Pat. No. 4,307,465 to Geller describes an “inductance or coil” which “functions as the antenna.” However, the coil is much smaller than the radiated wavelength and radiation efficiency is limited.
At microwave and millimeter-wave frequencies, small transmission line elements on a substrate or printed circuit board (PCB) function as quarter-wave radiating elements or as patch antennas. U.S. Pat. No. 6,366,245 to Schmidt and U.S. Pat. No. 6,107,955 to Wagner depict configurations for radiating from patch antennas coupled to dielectric lenses. These antennas are clearly separate from their active devices and their connecting leads.
As a drawback to these radiating devices, additional cost and complexity is incurred by utilizing antennas or coils to serve as the radiating devices. This also increases the size of the device and, due to inefficiencies or losses within such radiating devices or the conductive paths leading to such radiating devices, power consumption may be undesirably high.